JAVA泛型

当集合中存储的对象类型不同时，那么会导致程序在运行的时候的转型异常

package cn.nn;

import java.util.ArrayList;
import java.util.Iterator;

public class Generic_test {

    public static void main(String[] args) {
        ArrayList arr = new ArrayList();
        arr.add(new Tiger("华南虎"));
        arr.add(new Tiger("东北虎"));
        arr.add(new Sheep("喜羊羊"));

        System.out.println(arr);

        
          Iterator it = arr.iterator(); 
          while (it.hasNext()) {
              Tiger nextObject = (Tiger)it.next();
              Tiger tiger = nextObject; 
              tiger.eat();
          
          }
         
    }
}

class Tiger {
    String name;

    public Tiger() {

    }

    public Tiger(String name) {
        this.name = name;
    }

    public String toString() {
        return "Tiger@name:" + this.name;
    }

    public void eat() {
        System.out.println(this.name + "吃羊");
    }

}

class Sheep /*extends Tiger*/{
    String name;

    public Sheep() {

    }

    public Sheep(String name) {
        this.name = name;
    }

    public String toString() {
        return "Sheep@name:" + this.name;
    }
    public void eat() {
        System.out.println(this.name + "吃青草");
        
    }
}

出现 Exception in thread "main" java.lang.ClassCastException: cn.nn.Sheep cannot be cast to cn.nn.Tiger at cn.nn.Generic_test.main(Generic_test.java:19)错误。

package cn.nn;

import java.util.ArrayList;
import java.util.Iterator;

public class Generic_test {

    public static void main(String[] args) {
        ArrayList arr = new ArrayList();
        arr.add(new Tiger("华南虎"));
        arr.add(new Tiger("东北虎"));
        arr.add(new Sheep("喜羊羊"));

        System.out.println(arr);

        
          Iterator it = arr.iterator(); 
          while (it.hasNext()) {
              Tiger nextObject = (Tiger)it.next();
              Tiger tiger = nextObject; 
              tiger.eat();
          
          }
         
    }
}

class Tiger {
    String name;

    public Tiger() {

    }

    public Tiger(String name) {
        this.name = name;
    }

    public String toString() {
        return "Tiger@name:" + this.name;
    }

    public void eat() {
        System.out.println(this.name + "吃羊");
    }

}

class Sheep extends Tiger{
    String name;

    public Sheep() {

    }

    public Sheep(String name) {
        this.name = name;
    }

    public String toString() {
        return "Sheep@name:" + this.name;
    }
    public void eat() {
        System.out.println(this.name + "吃青草");
        
    }
}